The pathogenic processes that give rise to microangiopathic retinopathy and other vascular complications in diabetes are poorly understood. Several new lines of evidence have pointed toward inflammation as playing a heretofore unrecognized role. Retinal cells and vasculature and other self cells are protected from attack by autologous complement proteins by a set of intrinsic membrane regulatory proteins. These regulators are the decay accelerating factor (DAF or CD55), the membrane cofactor protein (MCP or CD46), and the membrane inhibitor of reactive lysis (CD59). Previous studies from our lab have shown that all three surface proteins are highly expressed in the retina and its associated vasculature in levels similar to those on glomerular cells and on systemic vasculature, sites where intrinsic regulatory activity is critical. In recent in vitro work, we have shown that DAF's regulatory function is 1) >90% inactivated by incubation with glucose or ribose, 2) rapidly abrogated by methylglyoxal incubation, and 3) lost due to modification of one or more active site lysine and arginine residues, the latter to argprymidine. In in vivo work, we have shown that endogenous DAF protein isolated from diabetic retinas is modified by several sugar adducts including argpyrimidine. The proposed studies are directed toward 1) determining the functional effects of chemical modifications in DAF, MCP, (and CD59) that are induced by hyperglycemia and other metabolic abnormalities that pertain in the diabetic state, 2) structurally characterizing the types and sites of the modifications on the regulators, 3) analyzing the functions and structures of endogenous DAF, MCP, (and CD59) proteins isolated from retinas and other tissues of diabetics, and 4) examining whether the pathological changes that are associated with retinopathy and other diabetic complications develop more rapidly in Daf1-/- (murine DAF homolog), Crry-/- (murine MCP surrogate), CD59a-/- (murine CD59 homolog) and double Daf1-/- / -/- Curry-/- or Daf1-/- / CD59a-/- mice experimentally made diabetic with streptozotocln. Since vasculopathy and retinopathy are debilitating complications that eventually affect most patients with diabetes, fully understanding the mechanisms involved in their development is important in designing effective therapeutic interventions.